The hallmark of type I diabetes is the loss of [unreadable]-cells. In order to develop therapies, we need to understand how these cells can be regenerated. The goal of this proposal is to understand how [unreadable]-cell regeneration is regulated. We have focused on PTEN (phosphatase and tensin homologue deleted on chromosome 10) and shown that deletion of Pten leads to increased islet mass. We hypothesize that PTEN deficiency increases islet mass by regulating [unreadable]-cell dynamics and plasticity. To test this hypothesis, we have set two specific aims. In Aim1, we will determine whether the effect of PTEN on islet mass is cell autonomous to [unreadable]-cells. Two approaches will be used to test the autonomous nature of PTEN on [unreadable]-cell regeneration. Lineage tracing using PtenloxP/loxP; RosalacZ; Rip-Cre+ mouse to investigate the role of PTEN in [unreadable]-cell proliferation will be the first approach. Previously, we have observed that PTEN deficiency leads to increased islet mass in conjunction with an increased proliferation near the islets. In this study, we will determine whether these proliferating peri-islet cells originate from [unreadable]-cells and whether they contribute to islet regeneration. To further test if the effect of PTEN is cell autonomous to [unreadable]-cells, we will determine whether the effect of PTEN on [unreadable]-cell regeneration is dependent on its role in development. To do this, we will use the PtenloxP/loxP; RosalacZ; Rip-CreER+ model that we have generated to induce Pten deletion in mature [unreadable]-cells. In Aim2, we will investigate the mechanism for PTEN induced [unreadable]-cell regeneration. We have observed increased mesenchymal cell formation in the Pten mutant pancreas. Since mouse [unreadable]-cells are most likely self regenerating, it is likely that these mesenchymal cells are [unreadable]-cells in the process of dedifferentiation as they do not express insulin. To address how PTEN regulates [unreadable]-cell plasticity, we will investigate the role of PTEN on epithelial mesenchymal transition (EMT) in [unreadable]-cell regeneration. EMT has been suggested to be one mechanism that [unreadable]-cells may use to regenerate. We will use lineage tracing with the PtenloxP/loxP; RosalacZ; Rip-Cre+ mouse to determine if these mesenchymal cells are indeed [unreadable]-cells going through EMT and whether they contribute to [unreadable]-cell regeneration. In summary, this application is focused on the mechanism of [unreadable]-cell regeneration. The result of this study will provide a mechanistic analysis of the feasibility of targeting the PI3K/AKT signal pathway in order to treat type I diabetes. The proposed study is focused on understanding the mechanism for pancreatic [unreadable]-cell regeneration. Stimulating [unreadable]-cell regeneration is an important goal for developing drug treatments targeted at type I diabetes. The proposed study provides a mechanistic analysis of the role of PTEN, a key growth regulator, in [unreadable]-cell regeneration. If the hypothesis is proven, this study will provide a molecular basis for drugs designed to target the PTEN regulated PI3K/AKT pathway in order to stimulate [unreadable]-cell regeneration. [unreadable] [unreadable] [unreadable]